1. Field of the Invention
The present invention relates to a turbo compressor capable of compressing a fluid by a plurality of impellers, and a refrigerator including the turbo compressor.
Priority is claimed on Japanese Patent Application No. 2008-27074, filed Feb. 6, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
As refrigerators which cool or freeze objects to be cooled, such as water, a turbo refrigerator or the like including a turbo compressor which compresses and discharges a refrigerant is known.
A turbo compressor included in the turbo refrigerator or the like generally includes a compression mechanism which rotates an impeller attached to a rotation shaft around an axis, and compresses a refrigerant. Conventionally, bearings which rotatably support the rotation shaft of such a compression mechanism around the axis are described in, for example, Japanese Patent Unexamined Publication No. 2002-303298, and Japanese Patent Unexamined Publication No. 2007-177695.
A configuration in which a compressor shaft (rotation shaft) is supported by angular contact ball bearings in a back-to-back state is disclosed in Japanese Patent Unexamined Publication No. 2002-303298. By supporting the rotation shaft by the angular contact ball bearings, the ball bearings can withstand a force applied to the rotation shaft in a thrust direction, and power can be transmitted efficiently with little power loss.
Additionally, a turbo compressor which includes two compression stages (compression mechanism) and which compresses a refrigerant sequentially in these compression mechanisms is disclosed in Japanese Patent Unexamined Publication No. 2007-177695. In this turbo compressor, two same impellers are fixed to the same rotation shaft such that their backs face each other. By supporting the rotation shaft by the journal bearings between the two impellers, an overhang load applied to the rotation shaft is reduced.
Meanwhile, in the turbo compressor, when a compression ratio may increase, the discharge temperature may become high and the volumetric efficiency may degrade. Therefore, the compression mechanism may perform compression of a refrigerant in a plurality of stages as described in Japanese Patent Unexamined Publication No. 2007-177695. In such a turbo compressor, the compressor is manufactured by combining a number of casings, and the rotation shaft is attached such that it is inserted through the casings.
However, the center of the rotation shaft may deviate due to eccentricity resulting from an accumulated error by an inevitable gap between the spigot portions of the casings for combining these casings together, or an allowance for the inclination of the rotation shaft may be exceeded in the bearings which support the rotation shaft. Particularly, the angular contact ball bearings in a back-to-back state disclosed in Japanese Patent Unexamined Publication No. 2002-303298 have high support rigidity but a small allowance for inclination. This becomes problematic. Additionally, when the distance between the bearings has become long by a combination of a number of casings, deflection by a gear reaction force or the like is apt to occur and the rotation shaft inclines. This becomes problematic.
Accordingly, the load by the inclination will act on the bearings in a normal state, and consequently there is a concern that the bearings receive fatigue and damage by the action, and their lifespan is shortened.